The present invention relates to a method for the target path correction of a load carrier approaching a target position, which load carrier is height-adjustably suspended on a horizontally movable lifting cable carrier via a lifting cable system.
Such methods in particular are used when containers for the cargo transport on ships or railways or on trucks are to be transported from a starting location to a target location and have to be brought in a particular position at the target location. With the expression particular position, i.e. for example an actual position or a target position, there may be meant
the location of a point of the respective container, PA1 the angular position of the respective container about a vertical axis and PA1 both the location of a point, for example the center, of this container and the angular position of the container about a vertical axis, for example the height axis of the container extending through the geometric center. PA1 a) in an end stage of the approach of the load carrier to the target position, the instantaneous values of a plurality of variable state values are determined in at least one point of time of detection. This plurality of state values comprises at least the following values: PA1 b) based on the instantaneous values determined in such a way the magnitude and the direction of the horizontal correction force for acting onto the load carrier can be determined, which force is necessary in order to reach the target position during the further course of the target approaching movement of the load carrier; PA1 c) then a variation of the cable course of at least one cable member running between the lifting cable carrier and the load carrier necessary for generating this correction force is calculated; PA1 d) the necessary variation of the cable course of the at least one cable member is generated by imparting a substantially horizontal movement onto a cable course influencing unit of the at least one cable member relative to the lifting cable carrier by cable movement means which are connected to the lifting cable carrier for a common transport movement which cable course influencing unit is arranged at or near said lifting cable carrier. PA1 firstly the determination of the instantaneous value difference of an actual position height coordinate of the load carrier and a target position height coordinate of the load carrier; PA1 secondly the determination of the instantaneous value difference between at least one actual position horizontal coordinate of the load carrier and an associated target position horizontal coordinate of the load carrier; PA1 thirdly the determination of the instantaneous value of a vertical approach velocity of the load carrier to the target position; PA1 fourthly the determination of the variation of the at least one actual position horizontal coordinate relative to the associated target position horizontal coordinate.
In particular when loading ships with containers, there arises the problem that the containers have to be brought from the respective starting point to the respective target position on the ship with a high speed of conversion. The target position in this case can be a particular stand on the deck of a ship or the entry of a container chute into which the respective container is to be lowered. These high speeds of conversion have to be attained because of economical reasons: the fees for the the dwell period of a ship in a harbor are high. The faster a ship can be loaded and unloaded the lower the necessary dwell periods of the respective ship are. Therefore, it is essential that the containers are not only brought from the starting location to the target location with a high transport velocity; it is further essential that in the end approaching stage of the container the accurate positioning of the container can be carried out the shortest possible period of time. It has to be taken into account that the containers on the deck of a ship have to be accurately disposed on the predetermined stands with respect to location and orientation. It is further understandable that the containers intended for storage in container receiving chutes of a ship have to reach the entry of the respective container receiving chute in an accurate geometrical registry with respect to this chute. This means that the actual position of the container, represented for example by the actual position of the geometrical center of the container, upon reaching the entry of the container chute has to be in accurate alignment with the center of the cross-sectional area of the container chute entry in a vertical direction and that further the actual angular position of the container outline about the height axis thereof has accurately to be in alignment with the angular position of the outline of the container chute entry. Only if these coincidences are secured, the respective container can be moved to its target position with high velocity. Only if these coincidences are fulfilled a container for example can be lowered at a high descent velocity through the entry of the container chute to its respective stand within the container chute.
The lowering paths a container has to run through during loading a ship are very long, for example in the magnitude up to 50 m. These lowering paths on the one hand are given by the substantial height of the container receiving chutes, and on the other hand and also in particular by the great height of the superstructures of ships, with which the containers, and in particular the crane constructions on which the load carriers are carrying out the transporting movements, must not collide. Imagine that such crane constructions normally comprise a tower-like crane travelling device or chassis movable along the edge of a quay and that on this tower-like crane chassis a bridge carrier is disposed which extends substantially orthogonal with respect to the quay edge. In order to be able to serve the container stands on the deck of the respective ships distributed over the entire horizontal cross-sectional area of the ship or in container receiving chutes within the respective ships, it is necessary to move the tower-like crane chassis with the bridge carrier in a longitudinal direction of the quay, such that the bridge carrier is adjustable above the respective container stands of the ship to be served and that the load carrier can be lowered to the respective stands. In order to enable the tower-like crane chassis to move in the longitudinal direction of the ship anchored to the quay edge it is necessary that the height of the bridge carrier on the tower-like crane chassis be above the top end of the highest ship superstructures. This leads to huge lowering paths of the load carriers coupled to the respective container. As the load carriers are suspended on lifting cable carriers movable on the bridge carrier via a length-variable lifting cable system, vibrations of the load carriers and of the containers coupled thereto have to be considered. These vibrations do not only arise from the movements of the lifting cable carrier along the bridge carrier, in particular from the starting and braking accelerations of the lifting cable carrier movable along the bridge carrier, but also arise from further influences, as for example wind influences. Even possible movements of the tower-like crane chassis in a longitudinal direction of the quay edge can lead to vibrations of the load carrier suspended on the lifting cable carrier via the lifting cable system.
There exist numerous proposals in order to allow the deposition of loads and in particular of containers in a correct position at the stands provided for them, for example on a ship. In particular, it has been tried to influence the course of a movement of a lifting cable carrier, for example of a trolley, along the bridge carrier of a crane by taking account of the target position and of exterior influences, for example a wind influence, such that the vibrations of the load carrier suspended on the lifting cable system upon entry of the load carrier into a vertically aligned position relative to the respective target position have substantially reached a standstill and the load carrier with or without container can then be lowered onto the stand without a substantial further correction of its lateral position and its orientation.
It has further been proposed, namely in EP-A-0 342 655 and the corresponding U.S. Pat. Nos. 5,048,703 and 5,152,408, to monitor the target position of the respective containers to be deposited by means of a detection device arranged on the load carrier and to carry out corrections of the lateral position and, if necessary additionally of the orientation of the respective containers to be lowered such that the container reaches its target position with high accuracy.
All attempts to enhance the aiming accuracy upon depositing a load, in particular a container, have been rendered difficult by the problem that it is impossible to impart a direct correction force action onto a load carrier suspended on a lifting cable system with or without load. It therefore was necessary to generate a positional correction of a load carrier suspended on a horizontally movable lifting cable carrier via a lifting cable system by means of movements of the lifting cable carrier, for example a trolley, along a bridge carrier. For doing so, the huge mass of the lifting cable carrier has to be moved by its transport drive. It has been found to be very difficult to move this huge mass sensitively enough to obtain the desired positional correction. The problem when loading a ship is even bigger when the positional correction has to be effected in the longitudinal direction of the quay, because in this case the entire mass of the crane structure, including the tower-like crane chassis, the bridge carrier, the trolley, the load carrier and the load has to be brought in a moving state by the transport drive of the crane chassis.
Even if the possibility of an approximate target correction of the respective load carriers has been reached with the aid of the transport drive of the trolley and/or the tower-like crane chassis by correspondingly powerful drives, this was only possible under the acceptance of huge accelerations upon effecting correction movements of the lifting cable carrier designed as a trolley and of the tower-like crane chassis. As normally an operator of the trolley is always present in order to supervise and possibly influence the loading operations, this operator until now has been continously subjected to these huge accelerations, in an amount which was above the tolerance limits and in particular above the officially prescribed limits.
From GB-A-1 557 640 it is known that in a crane apparatus for loading ships by means of a trolley and a spreader suspended on the trolley via cables, the suspension of the cable portion proximate to the trolley is provided by an intermediate carrier on the trolley which can carry out a creeping movement relative to the trolley. By the aid of this creeping movement a positional correction of the container which substantially is at a standstill should be made possible after the spreader has approached its target location at a point of time at which physical contact of the spreader and the container, respectively, to the target location, namely a container disposed below, via contact plates is possible, the correction being carried out by displacing this spreader and container, respectively, hanging on the intermediate carrier by means of the creeping movement of the intermediate carrier relative to the trolley until a stop has been reached, followed by terminating the creeping movement by means of an end switch in the abutment region.